A positioning technology is a technology adopted in order to determine a geographic location of a mobile station, and location information of the mobile station may be directly or indirectly obtained by utilizing a resource of a wireless communication network. Standard terminal positioning manners adopted in LTE (long term evolution) include the following three types: network assisted GNSS (global navigation satellite system) positioning; downlink positioning, or referred to as an OTDOA (observed time difference of arrival) manner; and e-CID (enhanced cell identification) positioning.
A mobile station positioning algorithm of the LTE may generally estimate a geometrical location of a mobile terminal by detecting characteristic parameters (such as signal field strength, propagated signal time difference of arrival, and signal direction angle of arrival) of a signal propagated through a radio wave between the mobile station and a base station, and then according to a relevant positioning algorithm. A GNSS positioning method requires that a terminal has a wireless receiver for receiving a GNSS signal, and specific implementation of the GNSS includes GPS (global positioning system) positioning, Galileo positioning, and the like. Both downlink positioning and e-CID positioning belong to a network positioning type, mainly depend on detection of a characteristic parameter of a radio resource in a mobile communication system, then estimate a location of a mobile station according to a positioning algorithm, and are a current research hotspot. With OTDOA positioning, downlink PRSs (positioning reference signal) are received from a plurality of base stations by utilizing a mobile station, measurement is performed at a fixed time, a PRS time difference of arrival between base stations is reported, and calculation is performed on a network positioning server to obtain a geographic location of the mobile station.
Currently, with continuous development of mobile communications technologies, demands for a positioning service are also increased day by day. Application scenarios of the positioning service are on a diversified trend, such as positioning of help seeking in emergency, crime location tracking, navigation and transportation control. However, no matter how the application scenarios are diversified, for demands for positioning, the industry always intends to obtain a reliable, effective, and rapid method; and in other words, a positioning technology that is easy to implement with high precision is a hotspot that people always chase after.
The OTDOA is a common positioning technology, and its principle is: when three or more than three base stations exist in a system, a location of a terminal may be determined according to a time difference of arrival between downlink transmission signals of different base stations. The downlink transmission signals may be reference signals, and may also be synchronization signals. In the LTE, the OTDOA positioning serves as a network assisted terminal positioning technology. After a network side e-SMLC (enhanced serving mobile location center) designates a sending and receiving configuration of a positioning reference signal (PRS) for a base station and a mobile station, the base station sends a PRS in the downlink, and the mobile station receives PRSs from a plurality of positioning base stations, identifies a first arrival path location of each PRS, may obtain a PRS time difference of arrival between different base stations, and reports the PRS time difference of arrival to the e-SMLC. The e-SMLC receives a signal time difference between different base stations through the mobile station, the signal time difference may be mapped into a distance difference between the mobile station and different base stations, and the e-SMLC may obtain an accurate location of the mobile station through mathematical calculation of a hyperbolic model. The OTDOA positioning has an advantage of highly precise positioning, and may be used to position a mobile station of a non-line-of-sight network.
However, the precision of the OTDOA positioning depends on estimation for reception and a first arrival path of a PRS signal to a large extent. Compared with the GPS, the OTDOA may complete terminal positioning in part of dense urban areas or indoor area scenarios, but because a time difference of arrival of a signal needs to be estimated and wireless propagation environments of both a dense urban area and an indoor area influence a multipath of the signal, the OTDOA cannot truly reflect a difference between straight line distances from two base stations to a UE, and in this way, a positioning error is increased. Furthermore, a situation that a downlink PRS is interfered greatly influences positioning precision, and therefore, what is discussed in a current standard is that a PRS is sent in a low interference subframe, that is, except an RE (resource element) of the PRS, an RE of a CRS (cell-specific reference signal) and a public channel, no RE of a data channel exists in a subframe of the PRS. However, A PRS pattern is shifted according to PCI (physical cell identifier) Mod 6 in a frequency domain, and therefore, when values of PCI Mod 6 of two cells are equal, co-channel interference exists between PRSs of the two cells. Therefore, muting is introduced into the Rel-9 protocol, and interference is avoided through separation in a time domain. However, the muting wastes an opportunity that a terminal receives a plurality of PRS time domain signals, and the positioning precision is influenced somewhat. Additionally, if values the PCI Mod 6 of the PRSs are different, although the PRSs of the two cells are mapped into different REs, when a difference between SNRs (signal to noise ratio) of the PRSs of the two cells is excessively large, orthogonality between different REs may be damaged, thereby causing that PRS interference between the different REs is generated, as shown in the following:
Length of RSTD ΔSNRSearch WindowError (Ts)10 dB320 Ts0.520 dB320 Ts0.530 dB320 Ts1.135 dB320 Ts1.840 dB320 Ts130
where RSTD represents a reference signal time difference, Ts represents a minimal time unit in an LTE system, and 1 Ts=1/(2048×15000) seconds.
When a PRS SNR difference between two cells (different PCIs) is greater than 30 dB, an RSTD (reference signal time difference) estimation error demand of the rel-9 cannot be satisfied. It is found through system-level simulation that, a situation that this difference is greater than 30 dB is not a small probability event, and therefore, current OTDOA muting needs to be enhanced, so as to cancel interference caused by PRSs of different REs.